1. Field of the Invention
The present invention relates to an oscillator circuit.
2. Description of Related Art
Heretofore, an oscillator circuit for realizing lower power consumption has been provided with a configuration as shown in FIG. 1A. This circuit is described specifically by referring to this figure. A CMOS inverter 101 is connected with a higher-potential power supply 103 and with a lower-potential power supply 104 via current-limiting devices 102 that are used to realize lower power consumption. One electrode of a load capacitor 105 is connected with the input side of the CMOS inverter 101, while the other electrode is connected with the lower-potential power supply 104. One electrode of a load capacitor 106 is connected with the output side of the CMOS inverter 101, whereas the other electrode is connected with the lower-potential power supply 104. Also shown are a quartz oscillator 107 and a feedback resistor 108.
In the above-described configuration, however, the load capacitors 105 and 106 directly connected with the power supplies cause the circuit to have the problem that the power-supply voltages vary greatly in synchronism with the oscillation. Therefore, any circuit using a power supply in common with this oscillator circuit has the disadvantage of becoming unstable in operation. Conversely, where the power-supply voltages are varied by some action independent of the oscillation, there is also the disadvantage that the variations adversely affect the oscillator circuit.
Where an oscillator circuit IC including a CMOS inverter having an externally attached quartz oscillator is connected with a buffer circuit IC, it is common practice to attach an AC coupling capacitor externally to an output of the CMOS inverter within the oscillator circuit and to connect the input terminal of the buffer circuit via the coupling capacitor.
A protective circuit is mounted to the input terminal portion of the buffer circuit. This protective circuit has an electrostatic capacity of about 5 pF. Accordingly, the electrostatic capacity of the AC coupling capacitor is required to be large enough to be capable of canceling out the electrostatic capacity of the protective circuit, e.g., approximately 100 pF. This increases the size of the AC coupling capacitor that must be attached externally. In consequence, the circuit scale is increased.